In the petrochemical industry, the production of binary copolymers with a defined content of C3H6 and C2H4, typically 8% C2H4 and 92% C3H6, belongs to the most strongly growing product ranges. Correspondingly, processes for the targeted production of these mixtures of C2H4 and C3H6 are of particular interest. Furthermore, attempts are made to use other raw materials instead of petroleum as starting material for the production of olefins on a medium- and long-term basis.
DE 197 23 363 A1 describes a process for producing C2- and C4-olefins by reacting a vaporous reaction mixture containing MeOH and/or DME and H2O in a first reactor on a form-selective catalyst with temperatures of 280 to 570° C. at pressures of 0.1 to 1 bar[a], wherein a product mixture containing C2- to C4-olefins and gasoline hydrocarbons (C5+) is withdrawn from the first reactor and a C5+-stream rich in separated gasoline hydrocarbons is evaporated, mixed with steam, the weight ratio of H2O to hydrocarbons is adjusted to 0.5:1 to 3:1, and the mixture produced with a temperature of 380 to 700° C. is introduced into a second reactor containing a form-selective catalyst and a product mixture is withdrawn, whose added content of C3H6 and butene isomers is at least 50 wt-% of the olefin constituents of the feed mixture supplied to the second reactor.
DE 100 271 59 A1 describes the so-called MTPO process for producing C3H6 from MeOH, in which vaporous MeOH is reacted on a first catalyst to obtain a first vaporous mixture containing DME and on a form-selective zeolite catalyst arranged in at least two series-connected adiabatic shaft reactors a product mixture containing C3H6 is produced, wherein a first partial stream of the first vapor mixture containing DME together with H2O vapor is guided into the first shaft reactor, from which a first intermediate product mixture is withdrawn and charged to the second shaft reactor. To the second shaft reactor a second partial stream of the DME-containing first vapor mixture is supplied and from the last one of the series-connected shaft reactors a product mixture is withdrawn, from which a fraction rich in C3H6 is separated. The remaining partly gaseous residue containing C2H4 and C4+-hydrocarbons is recirculated into one of the shaft reactors.
The subject-matter of US 2005/0107651 A1 is a process for producing a mixture containing MeOH and EtOH and for converting MeOH and EtOH to light olefins, wherein MeOH and EtOH with a weight ratio of 1 to 99% are supplied to a reaction zone in which MeOH and EtOH are reacted on a molecular sieve catalyst to obtain light olefins. In a similar process described WO 2005/051872 A1, the ratio of MeOH to EtOH in the feed stream is adjusted to 6 to 10.
DE 102 33 975 A1 deals with the production of C3H6 from MeOH, in which a vaporous mixture of MeOH, DME and H2O at operating temperatures of 250 to 460° C. is passed over a plurality of sequentially arranged reaction stages of an adiabatic reactor, which each are equipped with a form-selective zeolite catalyst with pentasil structure, and between the reaction stages cooling of the emerging reaction mixture takes place. After the last reaction stage, the cooled reaction mixture is separated into a gas phase and into a liquid phase chiefly containing water, and after a condensation the gas phase is separated into a gas phase containing hydrocarbons and into a liquid phase containing DME, MeOH and water, and thereafter C3H6 is removed from the gas phase. In an advantageous development of this process with regard to an improved heat guidance described in DE 102 006 026 103 A1, a process stream containing DME and MeOH as well as H2O is cooled and separated into a liquid phase and into a gas phase, the gas and liquid phases are split up into a plurality of partial streams, whose number each corresponds to the number of spaces present between the reaction stages, and the individual gas phase partial stream is each charged to a nozzle tube with a liquid phase partial stream and the liquid phase is sprayed into the corresponding space by means of the gas phase.
DD 257 740 A3 relates to a process for producing C2- to C4-olefins by converting gases containing CO and H2 to an alcohol mixture which contains MeOH and higher aliphatic alcohols in a mass ratio of MeOH to higher alcohols of 0.6 to 5.6, wherein the higher aliphatic alcohols are reacted on zeolitic catalysts with pentasil structure at temperatures of 250 to 600° C. and pressures of >100 kPa. By adjusting the indicated mass ratio between MeOH and higher alcohols, a heat compensation between exothermal MeOH conversion and endothermal dehydration of the higher alcohols largely is achieved during the conversion of the alcohol mixture on the conversion catalyst, which leads to an approximately thermoneutral reaction. The energy for the dehydration of the alcohol hence is provided by the MeOH conversion while simultaneously forming additional olefins. It is problematic, however, that with increasing retention time in the reactor the C2H4 formed from the fed EtOH is increasingly converted to other less valuable products such as olefins with more than four carbon atoms, paraffins, aromatics and/or naphthenes. In addition, there is the problem of the temperature control. When a product with a defined content of C3H6 and C2H4 is to be produced, an adiabatic temperature increase of 50 to 150° C. is obtained for the entire reaction. In a single-stage reactor the reaction accordingly passes through a wide temperature range. Since the selectivities for C3H6 and C2H4 increase with rising temperature, and on the other hand a maximum admissible temperature for the respective catalyst should not be exceeded, the reaction conditions become the more unfavorable the wider the temperature range passed through in the reactor becomes, with the consequence that the yield of target products is decreased.